The invention relates generally to wind turbine blade operation and more specifically to an aerodynamic device for detection of wind turbine blade operation.
Recently, wind turbines have received increased attention as an environmentally safe and relatively inexpensive alternative energy source. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted within a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 40 or more meters in diameter). Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid.
Operators of windfarms want the wind turbines to operate continuously and with maximum efficiency to provide the most return on their investment. Operational conditions that interfere with continuous operation and maximum efficiency are undesirable and should be avoided. Two operational conditions of the wind turbine blade that may interfere with the efficient operation of the blade and hence the wind turbine power output are blade icing and blade stall.
Under some atmospheric conditions, the rotor blades become covered with ice. Ice buildup typically occurs on the leading edge of the airfoil and causes a reduced lifting capability. As the ice layer becomes increasingly thick, weight is added to the airfoil so that the lifting airfoil surface becomes modified. For wind turbines, this modification can result in diminished aerodynamic rotor blade performance. This reduced performance can directly result in increased system loads and/or lost power output.
Buildup of ice on the blades can also create a serious hazard to personnel and equipment beneath the blades. Heavy ice formations on the blade may come loose during operation and fall to the ground from heights of 100 meters or more.
A motion of a wind turbine blade with respect to the wind divides an airflow between the pressure side and the suction side. The airfoil shape of the wind turbine blade causes faster flow over the suction side than the pressure side resulting lower pressure on the suction side than the on the pressure side, creating a net force on the blade resulting in motion of the blade (comparable to lift for an airplane wing). However, if the angle of attack of the blade with respect to the wind becomes too great, all of a sudden the airflow on the upper surface stops sticking to the surface of the wing. Instead the air whirls around in an irregular vortex (a condition which is also known as turbulence). Lift from the low pressure on the upper surface of the wing quickly disappears. This phenomenon is known as stall.
Stall may occur on different parts of the blade at different times based on the localized conditions. However, stall results in lower blade performance and consequently a lower power being generated by the wind turbine. If stall conditions occur over an increasingly greater portion of the blade, wind turbine power output will progressively degrade.
Accordingly, there is a need to provide a method for detection of abnormal operation due to ice buildup or stall conditions so as to be able to reduce downtime and enhance efficient operation for the wind turbine.